SSC Selection Post 2022 PYQ — Question 56

SSC Selection Post - Matriculation Level - 10 Feb 2022 - Shift 1 • Quantitative Aptitude • Q56

If x4+1x4x^4+\frac{1}{x^4} = 34 where x > 0, then find the value of (x+1x)(x+{1\over x}).

Show answer & explanation

Correct answer: C

Explanation

The correct answer is Option 3 i.e. 222\sqrt2.

x4+1x4x^4+\frac{1}{x^4} = (x2+1x2)2(x^2+{1\over x^2})^2 - 2

⇒ 34 = (x2+1x2)2(x^2+{1\over x^2})^2 - 2

⇒ (x2+1x2)2(x^2+{1\over x^2})^2 = 36

⇒ (x2+1x2)(x^2+{1\over x^2}) = 6

⇒ (x2+1x2)(x^2+{1\over x^2}) = (x+1x)2(x+{1\over x})^2 - 2

⇒ 8 = (x+1x)2(x+{1\over x})^2

⇒ (x+1x)(x+{1\over x}) = 222\sqrt2